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Acceleration Pickup
Transducer which generates output (generally, an electric signal) proportional to the input acceleration.
Acceleration Transducer
Synonym for acceleration pickup.
Coincidence of indicated value with approved standard value or desired value.
Note: The limit of error is used only as a qualitative concept.
Adjustable Range
Range of quantity adjustable by an adjuster.
Example: Zero adjustment, span adjustment, or bias adjustment.
Air Purge
Clean air externally supplied to the equipment for the following purposes:
(1) To prevent corrosive gages entering the equipment.
(2) To prevent temperature rise inside the equipment.
(3) To prevent explosive gases entering the equipment for flame proof construction, etc.
Allowable Error
Difference between the preset reference and the allowable limit value.
Allowable Load Resistance
Connectable load resistance within the range that the performance is guaranteed.
Amount of Unbalance
Quantitative scale of unbalance (on certain surface) in the rotor, and angular position is not considered.
It is also the product of unbalance mass and mass eccentricity.
Note: Unit of unbalance is g-mm, for example.
Maximal value of sinusoidal quantity.
Angle of Unbalance
Angle of location where unbalance mass exists with respect to the reference line in the polar coordinates system fixed in the plane perpendicular to the axial center line.
API Standard
Standard defined by the American Petroleum Institute.
(1) Reduction in signal size.
(2) Reduction in vibration amplitude with time.

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Maintaining vibration or force synchronous with the rotating speed within the specified limit by checking the rotor mass distribution and adjusting the distribution if necessary.
Bode Diagram
A pair of diagrams which show the amplitude ratio and phase shift with respect to frequency for a frequency response.

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To determine the equipment output corresponding to a series of known value of the quantity to be measure, received or transmitted.
Note: The following steps are conducted during actual calibration.
(1) To determine each position where a scale line is drawn on a scale plate.
(2) To perform adjustment to match the output with the desired value within an
      allowable error stipulated in the specifications.
(3) To determine the error by comparing the equipment output readings with
      the standard output values.
(4) Generally, calibration is performed to match independent quantities with
      the specifications.
Contact Capacity
Contact capacity expressed by the maximum allowable voltage applicable to the contact part and the maximum allowable current at which the contact part can be opened or closed.
Contact Input
Input of which the signal represents open/close state of an electrical contact.
Contact Output
Output signal generated by an electric contact opening or closing.
Contact Type
Contact type resulting from the difference between circuit configurations of switches, etc.
Single-pole normally open (SPNO) type.
Signal-pole normally closed (SPNC) type.
Single-pole double-throw (SPDT) type
Double-pole double-throw (DPDT) type.
Crest Factor
Ratio of the peak value to rms value.
Note: The crest factor of a sine wave is 2
Critical Speed
Rotating speed when a rotating system becomes resonant.
All states or values in the entire range followed by a cyclic phenomenon of function until returns to the previous status again.

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Damped Natural Frequency
Frequency of natural vibration in a linear system having attenuation.
Device to absorb energy to reduce the shock or amplitude.
Damping Ratio
Ratio of actual damping coefficient to critical damping coefficient in a system having linear Viscous Damping.
Note: The camping ratio is also expressed as a percentage to critical damping.
Delay Time
Time which characterizes the time lag.
Generally, this is expressed as the time until the tangential line drawn at the point with the sharpest gradient on the response curve of the output signal intersects with the time axis just after the step input signal is applied.
Note: This time is also called "effective dead time."
Differential Expansion
Measurement of dimensional changes of the gap between the rotor and casing which changes with the difference between the thermal expansion speeds of the rotor and casing.
Digital Signal
Signal having a parameter which gives a set of digitized values displayed numerically.
Displacement Pickup
Transducer which generates an output (generally, an electrical signal) proportional to the input displacement.
Dry Contact Output
Electric contact output which does not feed power to the contact part from the contact activation side.
Dynamic Characteristic
Response characteristics of equipment covering the input changing with time.

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Eccentricity P-P
The amount of rotor-shaft deflection produced when the rotor of rotating machinery is at a standstill caused by the dead weight of the rotor itself or at an uneven cooling speed.
Electromagnetic Interference
Unfavorable effect imposed on circuits and parts by an external magnetic field.
Note: Ratio frequency interference (RFI) is a well-known example.
Elliptical Vibration
Vibration whose vibrating points describe an elliptical locus.
Algebraic difference between a measured value and an ideal variable to be measured.
External force acting on the system or input.
Explosion Class
Explosion class or ignition temperature of explosive gases existing (or assumed to exist) in the hazardous area where the explosion-proof equipment is installed.
When equipment is installed in a hazardous area with explosive gases (inflammable gases or vapor generated from inflammable liquids), protection from explosion or fire caused by the equipment itself.
Explosion-proof Construction
Equipment designed to the explosion-proof.
Note: The following constructions are frequency used for explosion-proof construction of electrical equipment as industrial control equipment:
(1) Flameproof construction
(2) Intrinsically safe construction
(3) Combination of (1) and (2)
External Magnetic Field
Strength of magnetic field existing where the equipment is installed.
(Not the magnetic field generated by the equipment itself.)

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Failure Rate
Rate of failure of equipment or system operated until a certain period occurring within the succeeding unit of period.
Field Balancing
Balancing conducted using the bearing of the machine itself to be balanced and the support structure without using a balancing machine.
Flameproof Construction
Explosion-proof construction in which if explosive gases explode in a fully closed enclosure, it is tested and approved by a public agency that the enclosure can withstand the explosion pressure and does not produce flames which may ignite external explosive gases.
Flexible Rotor
Rotor which does not satisfy the definition of rigid rotor.
Flexural Critical Speed
Rotating speed at which one of the main flexural modes of the flexible rotor becomes a maximum. Rotor defection is more important than bearing displacement.
Flexural Principal Mode
Mode a rotor takes through flexural critical speed.
Flexural Vibration
Vibration appears as change in flexure of an elastic body.
Abbreviation of Factory Mutual Laboratories Standard defined by an American insurance company.
Form Factor
Ratio of the rms value to the mean value in a half cycle passing through two zero points.
Structure which supports a mechanical system.
Note: This may be fixed in space or may give excitation to the supported mechanical system by its motion.
Free Vibration
Vibration without excitation.
Note: In free vibration, a system vibrates at its natural frequency.
Number of cycles/second.
Frequency Analysis
Spectrum analysis of vibration phenomenon.
Frequency Response (Characteristic)
Time response of the output signal when the input signal changes sinusoidally.
Generally, it is expressed using a Bode diagram.
Fundamental Natural Mode of Vibration
Vibration mode having the minimum natural frequency.

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Terms for measurement:
JIS Z8103
Terms for performance of industrial instruments:
Japan Electrical Measuring Instrument
Industry Association
Vibration Engineering Handbook:
Terms for electronic measuring instrument:
Japan Electrical Measuring Instrument
Industry Association

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